In the Dáil on Tuesday night, Frances Fitzgerald said she could only "speculate" as to the reasons why one million breath tests would be faked.

The Tánaiste guessed it was the result of either "casual reporting", "ethical issues", "no supervision" or "collusion about the figures".

The options are pretty stark for Garda Commissioner Nóirín O'Sullivan, who will face a hostile Justice Committee in Leinster House today.

Patience in the Commissioner is running thin, even at Cabinet level.

She will have to provide at least a professional view of what has led us to a point whereby we can no longer trust the country's law enforcers to compile basic figures.

Her opening statement accepts that gardaí "recorded numbers that were false".

That in itself is a step forward - but will lead to other questions. How many individual gardaí were involved? And were they under pressure from superiors to bump up the statistics?

The Smithwick Tribunal into the events surrounding the killings of two RUC members issued a report in 2013 which alluded to a "misguided sense of loyalty" in An Garda Síochána.

Maybe that's the problem. Were officers so determined to make the force look good they bumped up the stats? That would be a best-case scenario for Ms O'Sullivan.

In contrast, a report by the Garda Inspectorate in late 2015 talks about staff being "concerned with 'self-preservation' rather than acting in the best needs of the organisation".

If 'self-preservation' was the motivation, then the Commissioner has an even bigger problem than imagined.

"At worst, this was deception. At best, this was incompetence," Ms O'Sullivan will argue before the committee today.

"Either way, it was individually and organisationally shameful, and will be seen to be shameful by the public and the thousands of gardaí around the country who operate every day to the highest ethical standards," she will say.

"We all take responsibility for this, and all take responsibility for establishing how this happened and ensuring it cannot happen again."

But there's a difference between taking responsibility and holding somebody accountable.

Given that breath tests were being faked "countrywide", it's inevitable that significant numbers, probably hundreds, of gardaí had some hand, act or part in the falsification of figures.

Could they now be subjected to a criminal investigation?

Hundreds more are likely to have turned a blind eye to what was standard practice.

Will they face internal sanction?

These are difficult questions to answer, but Ms O'Sullivan needs to at least show that she's willing to try.

In Leinster House everybody has a theory on how these type of crises play out. But yesterday key players in both Fine Gael and Fianna Fáil admitted they don't know what the end game is here.

They are unsure what purpose the Commissioner's resignation will serve beyond satisfying the baying mob.

In the background the Policing Authority seems to be very unhappy with the level of engagement from Garda management. It has a key role to play now.

The final line of the Commissioner's statement to the committee states: "And I will ensure that the people responsible at all levels will be held to account."